Re: [elixir-core:10911] [Proposal] Support for shorter @spec syntax

[Wiebe-Marten Wijnja]

I do not think we should change the language to make specs shorter.




As a side note, if people would like to try this out in their own code,
it is possible to do so without altering the language itself:

```
defmodule AlteredSpecSyntax do
  defmacro __using__(_opts) do
    original_module = module_defining_macro(__CALLER__, :@, 1)
    quote do

      import unquote(original_module), except: [@: 1]
      import AlteredSpecSyntax
    end
  end

  import Kernel, except: [@: 1]
  defmacro @ast do
    case ast do

      {:spec, _, expr} ->
        desugar(expr)
      # ... and pass others on unchanged
      _ ->

        quote do
          original_module.@(unquote(ast))
        end
    end
  end


  defp desugar(expr) do
    # Do whatever you want here :-)
    expr |> Macro.to_string |> Code.format_string! |> IO.puts


  end

  defp module_defining_macro(env, macro_name, arity) do
    env.macros
    |> Enum.filter(fn {_module, macros} -> macros[macro_name] == arity end)
    |> List.first({Kernel, nil})
    |> elem(0)
  end
end

# Example usage:
defmodule Foo do
  use AlteredSpecSyntax
  @spec a() :: 42
  def a(), do: 42
end

```

~Marten / Qqwy

On 02-06-2022 22:59, 'Andrey Yugai' via elixir-lang-core wrote:

One could even argue that having to repeat a 'too' long function name might nudge the programmer in the direction of re-thinking the naming of the function: Maybe there is a more descriptive name or location for the function? Maybe the function is trying to do too much and could be split up?       Module.put_attribute(__MODULE__, AlteredSpecSyntax.OriginalModule, unquote(original_module))       # Add special cases to all kinds of expressions you want to intercept...           original_module = Module.get_attribute(__MODULE__, AlteredSpecSyntax.OriginalModule)     # ... and return the AST you _actually_ want the module to include from here

I don't think there's much gain in fiddling with Elixir internals trying to modify special form, or writing new macro specifically to omit the left argument in `::/2` for function specs. Perhaps more profoundly, this would implicitly tie one spec to one function clause, which is kinda odd if you want to specify typespecs for all clauses before a function head.

-------- Original Message --------
On 2 Jun 2022, 17:16, Boris Kuznetsov < m...@achempion.com> wrote:


    Currently, if you want to add spec to functions, you have to use
    @spec with a function name to define all argument / response types:

    defmodule StringHelpers do
      @spec long_word?(word()) :: boolean()
      def long_word?(word) when is_binary(word) do
    String.length(word) > 8
      end
    end

    I think, it would be nice to reduce "visual noise" of spec
    definition by allowing to omit the data we already know.

    defmodule StringHelpers do
      @spec word() :: boolean()
      def long_word?(word) when is_binary(word) do
    String.length(word) > 8
      end
    end

    With this syntax, we can define argument and response types and
    automatically treat it as spec for following long_word?/1 function.

    What do you think?

    Also, in case of multiple arguments we can either wrap it in
    parentheses or just use a comma for separation.

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